Question: $ { {-1} \times \left[\begin{array}{rrr}{1} & {3} & {1} \\ {-2} & {1} & {2}\end{array}\right] = {?} } $
Explanation: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rrr}{-1}\times{1} & {-1}\times{3} & {-1}\times{1} \\ {-1}\times{-2} & {-1}\times{1} & {-1}\times{2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rrr}{-1} & {-3} & {-1} \\ {2} & {-1} & {-2}\end{array}\right]}$